Jessica Loriaux, Geert Lenderink, Stephan de Roode

(Extreme) Precipitation, Present and Future

Pier Siebesma

TU Delft & KNMI

siebesma@knmi.nl

Clouds play a crucial role in weather and climate

• Radiation balance

• Hydrological cycle

Global Mean Precipitation

Observations (CMAP)

Multimodel mean (CMIP3)

Source: IPCC AR4 2007

The Role of Dynamics

Adler et al. JAMC 2012

6Climate modeling

1.Change of Global Precipitation in a warming climate

Physical Basis (1) Clausius-Clayperon

2

ln

sds

s

TR

L

dT

ed

p

eq ss

Saturation specific humidity:

For constant Relative Humidity RH=qv/qs :

specific humidity qv will increase with 6~7% per Kelvin

Constant RH hypothesis confirmed in many studies for both models and observations:

i.e. Stephens (1990), Held and Soden (2006), Dai (2006)

Stephens and Ellis JCL 2006)

Global mean surface temperature vs water vapor amount for CMIP3 models: 1%/yr increase CO2 runs

7.4 % increase per Kelvin

But what about Precipitation?

Global Precipitation increases with only 2~3% per Kelvin

Global Energy Controls on Precipitation

Global Atmospheric Energy Balance: LPSR atmnet ,

Rnet,atm: net radiative loss from the atmosphere 97W/m2

P : Surface Precipitation 80W/m2

S : Surface Sensible Heat Flux 17W/m2

Relationships of the changes in a warming climate: PLSR atmnet ,

Increased radiative

coolingDecrease in sensible

heat flux

Increase Precip

Global Precipitation increases in order to compensate for the enhanced atmospheric cooling.

Concluding Remarks

• Water vapor increases with ~7%/K following Clausius Clayperon

• Global Precipitation increases with 2~3%/K

•The lower growth rate of precipitation can be attributed to the relation between the enhanced (clear sky) radiative cooling and the increased water vapor (“the curve of growth”) (i.e. Stephens and Ellis 2008, Lambert and Webb 2008)

• The different temperature relations for water vapor and precipitation has the consequence that the atmospheric branch of the hydrological cycle is slowing down.

But what about the geographical distribution of Precipitation Changes?

Models ΔP [IPCC 2007 WGI] for A1B scenario

(IPCC 2007)

Do the rich get richer? (Held and Soden 2006)

Is there a contrasting precipitation responses in wet and dry regions? Some limited observational evidence, e.g. Zhang et al. (2007) Nature

Netherlands on the borderline between mean positive/negative response

13Climate modeling

2. Change of (Extreme) Precipitation in a warming climate in the Netherlands

Climatology of mean summer precip in the Netherlands

Figure: 20-year moving average of mean, coastal and inland precipitation for summer in the Netherlands (Lenderink et al. 2008).

Figure: 20-year moving average of mean, coastal and inland precipitation for summer in the Netherlands (Lenderink et al. 2008).

Trend in the growth of the inland-coastal precipitation difference.

Due to warmer sea surface temperatures

But what about extreme precipitation?

Climatology of mean summer precip in the Netherlands

observations

• Take the de 90%, 99% , 99,9% percentiles of the most extreme precipitation sums

• Group them as a function of the (dewpoint) temperature.

• Use this (dewpoint) temperature as a proxy of how extreme precipitation changes in a warming climate.

Loriaux, Lenderink, Siebesma & de Roode (submited JCL 2013)

KNMI Precipitation Data Set: • 27 stations in the Netherlands:

• daily dataset: 1980-2010

• 10 min dataset: 2003-2011

Daily Precip Sum

7% increase per degree

Td

Pre

cip inte

nsi

ty (

mm

/day) 99.9%

99%

90%

observationsLoriaux, Lenderink, Siebesma & de Roode (submited JCL 2013)

Daily Precip Sum

7% increase per degree

Td

Pre

cip inte

nsi

ty (

mm

/day) 99.9%

99%

90%

observationsLoriaux, Lenderink, Siebesma & de Roode (submited JCL 2013)

Td

14% increase per degree

10 Minutes sum

Large Scale Precip Convective Showers

Interpretation of the Results

• Intuitively CC-scaling can be understood by assuming that the extreme cases are those in which the available water vapor gets squeezed out of the atmosphere effectively.

•But what about super CC scaling?

• Latent heat release creates buoyancy

• buoyancy is transformed into kinetic energy

• Resulting increasing vertical velocity induces convergence.

•Convergence is an extra source for moisture

z

qwdz

z

qwP s

z

z

st

b

Simple updraft model:

w

The Experiment

For each temperature perturbation calculate the fractional increase of precipation:

z

qw

z

qw

P

P

s

s

And break it down in a thermodynamic and a dynamical part:

zq

w

zq

w

zq

w

zq

w

P

P

s

s

s

s

Thermodynamic

part

Dynamical

part

Pre

cipi

tatio

n

Heavy frontal ra

in follows moistu

re (~7%/K)

Mean Precipitation linked to

radiation balance (~3%/K)

Light Precipitation (-?%/K)

Temperature

Heavy

Con

vect

ive

Rain

(14%

/K)

Summary:

Free after Richard Allen

Univ. Of Reading